Three stacks of this buff active will grant you 219 dodge rating total, or 4.84% chance to dodge. However, it will take at least 12 seconds into a fight to obtain three stacks (due to the cooldown on Shield of Righteousness). Also, it's worth noting that there's no maximum duration on the buff from the libram, so each new cast of Shield of Righteousness will refresh the duration, allowing it to be kept up throughout the duration of a fight, and even into new fights, much like the way Divine Plea acts when specced into Guarded by the Light.